Sunday, December 21, 2014

10 Things About December Solstice

1. It's Also Called Summer SolsticeThe December Solstice is also known as the Summer Solstice in the Southern Hemisphere, where it marks the longest day of the year in terms of sunlight. In the Northern Hemisphere, it is the shortest day of the year in terms of sunlight and is known as the Winter Solstice.

2. It's the Second Solstice of the YearSolstices happen twice a year - once around June 21 and then again around December 21. On the June Solstice, the Sun is directly overhead the Tropic of Cancer in the Northern Hemisphere, while on the December Solstice, the Sun directly shines over the Tropic of Capricorn in the Southern Hemisphere. The June Solstice is also known as the Summer Solstice in the Northern Hemisphere and Winter Solstice in the Southern Hemisphere.3. It Happens at a Specific TimeMost people celebrate the whole day as the December Solstice. In reality, however, the Solstice occurs at a specific time - when the Sun is exactly overhead the Tropic of Capricorn. In 2014, this will happen on December 21, at 23:03 (11:03 pm) UTC. For locations that are ahead of UTC, this event will occur on December 22. This is because of time zones difference.

4. The Solstice's Date VariesThe December Solstice can happen on December 20, 21, 22 or 23, though December 20 or 23 solstices are rare. The last December 23 solstice was in 1903 and will not happen again until 2303.

5. The Sun Stands StillThe term solstice comes from the Latin word solstitium, meaning the Sun stands still. This is because on this day, the Sun reaches its southern-most (or northern-most during the June Solstice) position as seen from the Earth. It seems to stand still at the Tropic of Capricorn (and Tropic of Cancer during the June Solstice) and then reverses its direction.6. It's the First Day of Astronomical WinterIn the Northern Hemisphere, astronomers and scientists use the December Solstice as the start of the winter season, which ends on the March Equinox. For meteorologists, on the other hand, winter began three weeks ago on December 1.

7. The Earth isn't Farthest From the SunDuring the Northern Hemisphere winter the Earth actually makes its closest approach to the Sun. Seasons have little to do with the Earth's distance to the Sun, but with how it spins around its own axis. As the earth revolves around the sun, it also rotates around its axis, which is tilted at an angle of 23.5 degrees.The direction of the tilt of the earth does not change as the Earth moves around the Sun - the two hemispheres point towards the same position in space at all times. What changes as the Earth orbits around the Sun is the position of the hemispheres in relation to the Sun - the Northern Hemisphere faces away from the Sun during the December Solstice, while the Southern Hemisphere tilts towards the Sun. The opposite happens around the June Solstice, when the Southern Hemisphere faces away from the Sun during the December Solstice, while the Northern Hemisphere tilts towards the Sun. This is why people in the Northern Hemisphere experience winter around December Solstice and summer during the June Solstice.In fact, the Earth is on its Perihelion - the point on the Earth's orbit closest to the Sun - a few weeks after the December Solstice.

8. Earliest Sunset Does Not Happen on This DayMost places in the Northern Hemisphere see their earliest sunset a few days before the Solstice and their latest sunrise a few days after the Solstice. This happens because of the difference between how we measure time using watches and the time measured by a sundial.

9. Daylight Hours Increase Faster at Northern LatitudesIf you are in the Northern Hemisphere, the increase rate of daylight hours depends on your location's latitude - in more northern latitudes you will see a rapid increase in daylight hours compared to if you're in the more southern latitudes.